Gamma correction is needed to deal with luminance change or the like caused by age deterioration of a liquid crystal panel, a backlight, or the like of a monitor.
Patent Document 1 discloses a light measurement device with a swing arm. The light measurement device is moved to a position in front of a liquid crystal display device when measuring light, and is rotatably moved into a bezel when the light measurement is finished. Gamma correction is performed on the basis of the obtained screen light.